Field of the Invention
The present invention relates to a determination method of determining the exposure conditions of an exposure apparatus, a storage medium, and an information processing apparatus.
Description of the Related Art
An exposure apparatus which projects and transfers the pattern of a mask (reticle) onto a substrate (for example, a wafer) via a projection optical system is employed to fabricate a semiconductor device using a photolithography technique. In recent years, with miniaturization of semiconductor devices (that is, with a reduction in circuit line width), a demand has arisen for a technique which further improves the resolution of the exposure apparatus.
The exposure apparatus is required to transfer the pattern (its image) of a mask to a desired position on a substrate in a desired shape. However, due to some error factors during exposure, the mask pattern is often transferred to a position deviated from the desired position in a shape deviated from the desired shape. Examples of the error factors include the amount of exposure and the focus position in exposing the substrate. Note that examples of factors which cause the amount of exposure to deviate from an ideal state include instability of a light source and nonuniformity of the illuminance distribution in the illumination region. Examples of factors which cause the focus position to deviate from an ideal state include instability of the position at which the substrate is held, and unevenness of the substrate.
Also, the aberration of the projection optical system is one of the above-mentioned error factors. The projection optical system includes an aberration adjusting mechanism for adjusting (correcting) its aberration, as disclosed in International Publication WO 02/054036. International Publication WO 02/054036 discloses an aberration adjusting mechanism for adjusting the aberration of the projection optical system by driving an optical element, which forms the projection optical system, in an amount corresponding to the wavefront aberration of light having passed through the projection optical system. Such an aberration adjusting mechanism mainly has a function of adjusting low-order aberrations and is used to suppress generation of low-order aberrations and compensate for a temporal change in aberration. The aberration adjusting mechanism is also sometimes used to suppress the differences in image performance among individual image heights because the aberration exhibits different characteristics for each image height of the projection optical system. However, the capability of the aberration adjusting mechanism has a given limit, so the projection optical system generally has residual aberrations. Also, the amount of residual aberrations and the amount of fluctuation in aberration (that is, the amount of fluctuation in residual aberration due, for example, to exposure heat) during exposure vary in each individual exposure apparatus.
On the other hand, to further improve the resolution of an exposure apparatus, Japanese Patent No. 4606732 proposes a technique of optimizing (determining) the exposure conditions of the exposure apparatus. As an example of this technique, a technique (called the “SMO technique”) of optimizing both the mask pattern (its dimension and shape) and the effective light source shape (the light intensity distribution formed on the pupil plane of an illumination optical system) is available. In the general SMO technique, the mask pattern and the effective light source shape are adjusted to satisfy a reference value (target value) for the image performance such as the line width. Japanese Patent No. 4606732 also discloses a technique of optimizing the effective light source shape after setting a specific value (a nonzero value such as a value corresponding to residual aberrations) to the aberration of the projection optical system. As described above, the SMO technique of optimizing the effective light source shape and the mask pattern in consideration of the aberration of the projection optical system is available.
However, the conventional SMO technique which takes into consideration of the aberration of the projection optical system simply optimizes the effective light source shape and the mask pattern so as to compensate for the influence that the aberration of the projection optical system exerts on the image performance. Therefore, if simply adjusting the effective light source shape and the mask pattern is insufficient to compensate for the influence that the aberration of the projection optical system exerts on the image performance, it is impossible to determine the effective light source shape and the mask pattern so that the image performance satisfies the reference value. Since such a problem becomes conspicuous as miniaturization of semiconductor devices progresses, the conventional SMO technique is becoming insufficient to optimize the exposure conditions.